The present invention relates to a method of manufacturing reversible heat-sensitive recording medium and a reversible heat-sensitive recording medium obtained by this method of manufacturing reversible heat-sensitive recording medium.
With respect to a variety of cards including ID cards, pre-paid cards, etc., for instance, a reversible heat-sensitive recording medium with reversible heat-sensitive recording materials provided in layers has been adopted along with a magnetic recording, for a reversible heat-sensitive recording medium is capable of repeatedly erasing and/or writing information for the purpose of indicating an account balance, etc. Such reversible heat-sensitive recording medium does not require any developing process, and further, it has a high color-developing density. What is more, it is inexpensive and widely used.
In such a reversible heat-sensitive recording medium used for cards etc., erasing and/or writing process is implemented by heating a reversible heat-sensitive recording layer by a thermal head, etc. at a certain temperature in order to develop or erase colors such that desired characters, etc. can be displayed.
In order to protect the reversible heat-sensitive recording layer from any mechanical and physical stresses when coloring and discoloring by heating, it has been typical to adopt a protective layer on the surface of the reversible heat sensitive recording layer. By applying such protective layer, it is possible to improve the durability of the reversible heat-sensitive medium containing the reversible heat-sensitive recording layer, causing it to be able to last against repeated printing and erasing by heat.
It has been a problem that when printing or erasing, dirt, etc. on the surface of the reversible heat-sensitive recording medium and dust, etc. from the surrounding environment stick to the thermal head, etc., which conducts the thermal recording, cause scratches, sticking, etc. on the printing surface of the reversible heat-sensitive recording medium. Furthermore, another problem would be a bad visibility of printed characters due to glaring on the surface caused by the protective layer being highly smooth.
In view of the foregoing, the inventors of the present invention have proposed a reversible heat-sensitive recording medium as disclosed in Japanese Patent Laid-Open Publication No. 10-309869, which resolves all the above-mentioned problems. A reversible heat-sensitive recording medium capable of overcoming the above-mentioned problems is made possible due to such invention of a reversible heat-sensitive recording medium having a protective layer.
On the other hand, in recent years, there has been a growing need for forming a reversible heat-sensitive recording layer for credit cards, IC cards, etc. in order to show certain information, and therefore, the reversible heat-sensitive recording layer is constructed as applied to a transfer sheet or an adhesive sheet to be formed on the substrate sheet of a medium such as a card, etc. in an approximate flush state by being welded to the substrate sheet, etc. (adhered to the substrate sheet, etc. through heat fusion). Therefore, sometimes, the heating and pressurizing at the time of heat fusing cause the protective layer provided to the transfer sheet and the adhesive sheet together with the reversible heat-sensitive recording layer to become nearly like a mirror surface, eventually causing the above-mentioned problems of causing stains on the thermal head, scratchy printed characters, and low visibility due to sticking and glaring on the surface of the protective layer.
It is an object of the present invention to provide a reversible heat-sensitive recording medium and a method of manufacturing it, the reversible heat-sensitive recording medium provided as being invulnerable toward scratches, etc. even when printing/erasing is repeated under situation of dirt and dust attached to the reversible heat-sensitive recording medium, thus having improved durability against repeated printing/erasing. The inventors of the present invention have come to a completion of the invention as a result of their pursuit of developing a method of manufacturing reversible heat-sensitive recording medium, including a welding process, effectively using an unevenness of the surface of the protective layer.
In accordance with a first aspect of the present invention, there is provided a method of manufacturing reversible heat-sensitive recording medium having a reversible heat-sensitive recording layer and a substrate sheet, wherein a reversible heat-sensitive recording sheet or a reversible heat-sensitive recording transfer sheet having the reversible heat-sensitive recording layer is applied to the substrate sheet through welding, after which a protective layer is formed on the reversible heat-sensitive recording layer.
In accordance with a second aspect of the present invention, there is provided a method of manufacturing reversible heat-sensitive recording medium as mentioned in the first aspect, wherein the protective layer contains porous filler.
In accordance with a third aspect of the present invention, there is provided a method of manufacturing reversible heat-sensitive recording medium as mentioned in the second aspect, wherein an average particle diameter of said porous filler is within the range of 0.7-2.5 times of a thickness of said protective layer.
In accordance with a fourth aspect of the present invention, there is provided a method of manufacturing reversible heat-sensitive recording medium as mentioned in the first aspect, wherein the reversible heat-sensitive recording sheet or reversible heat-sensitive recording transfer sheet does not have a protective layer.
In accordance with a fifth aspect of the present invention, there is provided a method of manufacturing reversible heat-sensitive recording medium as mentioned in the fourth aspect, wherein the reversible heat-sensitive recording layer is composed of a leuco dye, a color developing/reducing agent, and a binder resin as its main constituents.
In accordance with a sixth aspect of the present invention, there is provided a method of manufacturing reversible heat-sensitive recording medium having a reversible heat-sensitive recording layer and a substrate sheet, wherein a reversible heat-sensitive recording sheet or a reversible heat-sensitive recording transfer sheet having the reversible heat-sensitive recording layer is applied to the substrate sheet through welding, after which a protective layer is coated on said reversible heat-sensitive recording layer, the protective layer having a surface roughness within a range of Ra values 0.10-0.60 xcexcm, the Ra values prescribed by JIS B 0601.
In accordance with a seventh aspect of the present invention, there is provided a reversible heat-sensitive recording medium, wherein a protective layer is formed on a reversible heat-sensitive recording layer of a welded product of a reversible heat-sensitive recording sheet or a reversible heat-sensitive recording transfer sheet having the reversible heat-sensitive recording layer and a substrate sheet through welding, the protective layer having a surface roughness within a range of Ra values 0.10-0.60 xcexcm, the Ra values prescribed by JIS B 0601.
In this kind of reversible heat-sensitive recording medium of the present invention, since the protective layer is formed on the reversible heat-sensitive recording layer of the welded product of the reversible heat-sensitive recording sheet or reversible heat-sensitive recording transfer sheet and the substrate sheet, microscopic unevenness on the surface of the protective layer will not be destroyed.
Consequently, it is possible to provide a reversible heat-sensitive recording medium invulnerable toward scratches, etc. even when printing/erasing is repeated under situation of dirt and dust attached to the surface of the reversible heat-sensitive recording medium. Furthermore, due to the protective layer formed in accordance with the present invention, it is possible to prevent the thermal head from having dirt, etc. attached thereto, and it is further possible to prevent the thermal head from microscopic scratches, etc.